Axial flow fan

ABSTRACT

Disclosed is a axial flow fan of an outdoor unit of an air conditioner. The axial flow fan comprises a hub connected with a rotational shaft of a motor; and at least one blade contacting the hub, wherein the blade has a part from the hub to a predetermined portion of the blade among a whole part from the hub to an outer end of the blade, and the other part from the predetermined portion of the blade to the outer end of the blade, the part being equally applied at a predetermined rake angle, and the other part being raised in a direction of a pressure surface of the blade, and wherein a ratio of an inner diameter and an outer diameter of the axial flow fan is between about 0.35 and about 0.4.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axial flow fan of an airconditioner, in which the number of blades is two, and each blade has apart from the hub to a predetermined portion of the blade among a wholepart from the hub to an outer end of the blade which is equally appliedat a predetermined rake angle, and the other part from the predeterminedportion of the blade to the outer end of the blade which is raised in adirection of a pressure surface of the blade, and a ratio of an innerdiameter and an outer diameter of the axial flow fan is between about0.35 and about 0.4.

2. Background of the Related Art

In general, an air conditioner is mounted therein with a refrigeratingcycle system composed of a compressor, a condenser, a capillary tube, anevaporator and a heat exchanger. The air conditioner is an apparatus forproperly sending cold air formed at the evaporator or warm air generatedat the condenser according to an indoor condition, and thus geniallymaintaining indoor atmosphere.

The air conditioner may be divided into a window type air conditionerwhere the refrigerating cycle system is mounted in a single body, aspilt type air conditioner where an indoor unit and an outdoor unit areseparated and installed indoors and outdoors respectively, and so forth.Particularly, the spilt type air conditioner is again divided, accordingto an installation method, into a wall-mounted type, a permanent-mountedtype (including a package air conditioner), a ceiling-mounted type, aceiling-embedded type and so on. Especially, the indoor unit of thespilt type air conditioner may has a structure capable of alternativelyusing the wall-mounted type and the permanent-mounted type and beingsimultaneously applied as the ceiling-mounted type according to need ofa user, which is referred to as a convertible type indoor unit.

FIG. 1 schematically shows a general air conditioner.

Referring to FIG. 1, the conventional air conditioner is composed of anoutdoor unit 20 which is disposed outdoors and exchanges heat withoutdoor air, an indoor unit 10 which is disposed indoors and conditionsindoor air, and a connecting line 30 which connects the outdoor unit andthe indoor unit with each other.

To be more specific, the outdoor unit 20 is a means for converting a gasrefrigerant of low temperature and low pressure, which is inputted fromthe indoor unit 10 by exchanging heat with the outdoor air, into aliquid refrigerant of low temperature and low pressure, and is composedof a compressor 11, a condenser 12 and an expansion valve 13.

Further, the compressor 11 is a component for converting the gasrefrigerant of low temperature and low pressure, which is inputted fromthe indoor unit 10, into the gas refrigerant of high temperature andhigh pressure, and the condenser 12 is a component for converting thegas refrigerant of high temperature and high pressure into a liquidrefrigerant of middle temperature and high pressure, and the expansionvalve 13 is a component for converting the liquid refrigerant of middletemperature and high pressure into the liquid refrigerant of lowtemperature and low pressure.

Here, the condenser 12 is a component for directly exchanging the heatwith the outdoor air, and has a separate fan for introducing the outdoorair.

Meanwhile, the indoor unit 10 lowers an indoor temperature by means ofevaporation, which occurs when the liquid refrigerant of low temperatureand low pressure introduced from the outdoor unit 20 is converted intothe gas refrigerant of low temperature and low pressure.

The indoor unit 10 is composed of an evaporator 21 and a fan 21 a,wherein the evaporator 21 converts the liquid refrigerant of lowtemperature and low pressure into the gas refrigerant of low temperatureand low pressure. The connecting line 30 is a component for connectingthe indoor unit 10 and the outdoor unit 20 to circulate the refrigerant,and is properly disposed according to a distance between the outdoorunit 10 and the indoor unit 10.

As set forth above, the outdoor unit 20 of the split-type airconditioner includes the compressor, the condenser, a cooling fan(hereinafter, referred to as “axial flow fan”) which usually generatemany noises, and a driving motor for rotating the axial flow fan. Theindoor unit 10 includes the evaporator 21 and the blow fan 21 a, andperforms refrigeration and circulation of the indoor air.

FIG. 2 is a perspective view illustrating a general split type airconditioner.

As shown in FIG. 2, the indoor unit 10 and the outdoor unit 20 areconnected to each other by the connecting line 30.

Meanwhile, the axial flow fan 40, as shown in FIG. 3A, has a hub 42coupled to a rotational shaft of the driving motor (not shown), and aplurality of blades 44 formed on an outer circumferential surface of thehub 42, wherein the hub 42 is integrally formed with the blades 44.

When the axial flow fan 40 is rotated by the driving motor, a pressuredifference is generated between front and rear sides of the plurality ofblades 44 formed on the outer circumferential surface of the hub 42.

This pressure difference generates a suction force capable of sucking upthe air, thus sucking up the outdoor air toward the outdoor unit 20through the suction. Thus, the outdoor air passes through the condenser12 provided on an intake side of the outdoor unit. At this point, theoutdoor air exchanges the heat with the gas refrigerant flowing throughthe condenser to condense the gas refrigerant into a liquid state, andthen flows out outside the outdoor unit 20 through ventilation of theaxial flow fan 40.

As for characteristic factors determining a ventilation characteristicof the axial flow fan 40, they are divided into two types: generalfactors such as the number of the blades 44, a (outer) diameter D of theaxial flow fan, a (outer) diameter d of the hub and so forth, andso-called blade factors such as a pitch angle β, a peak point of thecamber P, a maximum quantity of the camber MC, a length of a chord, asweep angle α and so forth at the blade, which will be described belowwith reference to FIGS. 3A and 3B.

The pitch angle β of the blade, as in FIG. 3B, is an angle between aflow direction of the fluid or the air (x-axis in the figure) and astraight line, namely a chord, running from a leading edge (L.E) of theblade 44 and its trailing edge (T.E).

Here, the quantity of the camber refers to a length joining the camber(a central line across a cross section of the blade) and the chord. Themaximum point of the camber quantity, i.e., the maximum quantity of thecamber MC, as in FIG. 3B, refers to the camber quantity between the L.E.of the blade 44 and the camber peak point P on the chord C running fromthe L.E to the T.E.

The sweep angle α refers to an angle between two lines that intersect,one of which is one which connects the center of an inner end of theblade 44 or the center of a portion where the blade 44 comes intocontact with the hub 42 but goes with a curvature of the blade 44, andthe other is one (Y axis in the figure) which passes through the center(point) of the inner end of the blade 44 and the center (point) of thehub 42.

Especially, the sweep angle α is a factor determining a noise of anairflow of the axial flow fan 40. When the sweep angle α is great, aphase difference of the airflow between the hub 42 and a tip of theblade 44 becomes great. In contrast, when the sweep angle α is great,the phase difference of the airflow becomes small.

The phase difference of the airflow causes a phase difference between anoise generated at the outer end of the blade 44 and a noise generatedat the inner end of the blade 44. The greater this noise phasedifference is, the lower a frequency of the airflow passing through theblade 44 becomes. Hence, the noise becomes lower.

And, the number of the blades 44 is an important factor determining theairflow noise generated when the axial flow fan 40 is operated.

One example of this conventional axial flow fan 40 is disclosed inKorean Patent Publication No. 2003-14960, titled AXIAL FLOW FAN OFOUTDOOR UNIT OF AIR CONDITIONER, previously filed by the presentapplicant and published as of Feb. 20, 2003. As for the disclosed axialflow fan of the outdoor unit of the air conditioner, it includes a hub42 connected with a rotational shaft of a motor and a plurality ofblades 44 integrally formed on an outer circumferential surface of thehub, wherein the number of the blades 44 is set to three, a whole outerdiameter of the fan is set to 340±2 mm, and a diameter of the hub 42 isset to 100±2 mm.

Further, each blade 44 is configured so that the pitch angle β islinearly changed from the hub 42 to the end thereof in a range between20 degrees and 37 degrees.

Each blade 44 is also configured so that the peak point of the camber Pis formed at a point corresponding to 70% of the chord length in adirection from the L.E thereof to the T.E thereof, and that the maximumquantity of the camber MC is set to 0.5% within each radius from the hub42 to the end of the blade 44.

Further, the sweep angle α of each blade 44 has a range between 47degrees and 49 degrees when a dimensionless radius coordinate is lessthan 0.3 and is linearly increased when the dimensionless radiuscoordinate exceeds 0.3 to have a range between 55 degrees and 57 degreesat the end of the blade.

For reference, the dimensionless radius coordinate is a factor fortaking into consideration of performance of the axial flow fan only bythe blades 44 except for the hub 42, and is determined between 0 and 1when a position where the blades and the hub come into contact with eachother is set to 0, and the end of each blade 44 is set to 1.

The dimensionless radius coordinate is obtained by the follow formula.r=(R−Rh)/(Rt−Rh), where R is the length from the center of the axialflow fan (i.e. the center of the hub) to a certain position, Rh is theradius of the hub 42, Rt is the length from the center of the axial flowfan (i.e. the center of the hub) to the end of each blade 44, namely,the radius of the axial flow fan.

According to the axial flow fan 40 having three blades 44 in the outdoorunit of the foregoing air conditioner, as shown in FIGS. 4 and 5, apressure coefficient and constant pressure efficiency are enhanced ascompared to another conventional axial flow fan having four blades. As aresult, the motor for the axial flow fan having three blades can be alsoenhanced in operation efficiency at an operation point, and can bedriven with a size smaller than that for another conventional axial flowfan having four blades. In addition, the motor for the axial flow fanhaving three blades is reduced by about 22% in consumption electricalpower required for operation.

However, when the axial flow fan 40 is driven, a slip stream or wakecomponent is generated at the L.E and T.E of the leading blade 44, and aturbulent flow component is generated by separation on a negativepressure surface. These two components have influence on the trailingblade 44, thus deteriorating the performance of the axial flow fan 40,and simultaneously generating the noise by a turbulent flow.

SUMMARY OF THE INVENTION

Therefore, an objective of the present invention is to design an axialflow fan within an optimal design range capable of suppressing increasein intensity of a turbulent flow generated from a surface of each blade,increase in thickness of a boundary layer on the surface of each bladeand disturbance of an airflow within a region of the hub.

It is another objective to provide an axial flow fan capable ofremarkably reducing a noise within the predetermined frequency range(between about 300 Hz and about 1000 Hz) with respect to the same airvolume as the conventional axial flow fan.

To achieve the above objective, the present invention provides an axialflow fan comprising a hub connected with a rotational shaft of a motor;and at least one blade contacting the hub, wherein the blade has a partfrom the hub to a predetermined portion of the blade among a whole partfrom the hub to an outer end of the blade, and the other part from thepredetermined portion of the blade to the outer end of the blade, thepart being equally applied at a predetermined rake angle, and the otherpart being raised in a direction of a pressure surface of the blade.

Further, the axial flow fan has a ratio of an inner diameter and anouter diameter of the axial flow fan between about 0.35 and about 0.4.

Therefore, according to the present invention, the axial flow fan canreduce the noise as low as possible and increase the pressurecoefficient and the constant pressure efficiency compared to theconventional axial flow fan.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, features and advantages of the present invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings, in which:

FIG. 1 schematically shows a general air conditioner;

FIG. 2 is a perspective view illustrating a general split type airconditioner;

FIGS. 3A and 3B are front and side views of a conventional axial flowfan, respectively;

FIG. 4 is a graph showing comparison of relation between a pressurecoefficient and a flow rate coefficient in a conventional axial flow fanwith that of another conventional axial flow fan;

FIG. 5 is a graph showing comparison of relation between constantpressure efficiency and a flow rate coefficient in a conventional axialflow fan with that of another conventional axial flow fan;

FIGS. 5A and 5B are front and side views of an axial flow fan accordingto the present invention, respectively;

FIGS. 7A and 7B show a state where blades are tilted on an outercircumferential surface of a hub at a certain rake angle in axial flowfans according to the prior art and the present invention;

FIG. 8 is a graph showing a state where a noise is changed according toa change of a solidity with respect to axial flow fans of the prior artand the present invention;

FIG. 9 is a graph showing a state where a noise is changed according toa change of a quantity of a camber with respect to axial flow fans ofthe prior art and the present invention;

FIG. 10 is graph showing relation between a (constant) pressurecoefficient, a constant pressure efficiency and a flow rate coefficientwith respect to axial flow fans of the prior art and the presentinvention; and

FIG. 11 is a graph showing comparison of a state where a noise ischanged according to a change of a frequency of an axial flow fan of thepresent invention with that of an axial flow fan of the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An exemplary embodiment of the present invention will now be describedwith reference to the accompanying drawings.

FIGS. 6A and 6B are front and side views of an axial flow fan accordingto the present invention, respectively. FIGS. 7A and 7B show a statewhere blades are tilted on an outer circumferential surface of a hub ata certain rake angle in axial flow fans according to the prior art andthe present invention.

An axial flow fan 140 of an outdoor unit of an air conditioner accordingto the present invention is composed of a hub 142 connected with arotational shaft 141 of a motor, and a plurality of blades 144integrally formed on an outer circumferential surface of the hub 142.

The axial flow fan 140 is configured so that the number of the blades istwo, that a ratio of an inner diameter to an outer diameter (i.e. aratio of the outer diameter of the hub and the outer diameter of thefan) is between about 0.35 and about 0.4, that a solidity, a ratio ofthe whole area of the fan 140 and an area of the blades, has a range of0.85±0.05, and that a quantity of a camber of the hub 142 has a range of5.0%±1.0%.

Hereinafter, a detailed description will be made on the axial flow fanof the outdoor unit of the air conditioner according to the presentinvention.

Meanwhile, when the axial flow fan 140 is driven, a slip stream or wakecomponent may be generated at a leading edge (L.E) and a trailing edge(T.E) of the leading blade 144, and a turbulent flow component may begenerated by separation on a negative pressure surface. These twocomponents may have influence on the trailing blade 144, thusdeteriorating performance of the axial flow fan 140, and simultaneouslygenerating a noise by a turbulent flow. Thus, the present invention aimsat preventing the drawbacks of the axial flow fan 140.

Further, the present invention is to suppress increase in intensity ofthe turbulent flow generated from a surface of each blade 144, increasein thickness of a boundary layer on the surface of each blade 144, anddisturbance of an airflow within a region of the hub 142.

In order to accomplish the objectives, the axial flow fan 140 is formedso that the number of the blades 144 is two, that the ratio of the innerdiameter to the outer diameter (i.e. the ratio of the outer diameter ofthe hub and the outer diameter of the axial flow fan) is between about0.35 and about 0.4, that the solidity, the ratio of the whole area ofthe fan 140 and the area of the blades, has the range of 0.85±0.05, andthat the camber quantity of the hub 142 has the range of 5.0%±1.0%. Withregard to this, the detailed configuration of the present invention isas follows.

The axial flow fan 140 of the outdoor unit of the air conditioneraccording to the present invention, as shown in FIG. 6A, is composed ofthe hub 142 connected with the rotational shaft 141 of the motor, andthe plurality of blades 144 integrally formed on the outercircumferential surface of the hub 142.

Here, the number of the blades 144 is set to two. The inner and outerdiameter ratio of the axial flow fan 140, i.e. the ratio of the outerdiameter of the hub 142 and the outer diameter of the axial flow fan140, is set to a range between about 0.35 and about 0.40.

Further, the ratio of the whole area of the axial flow fan 140 and thearea of the blades, i.e. the solidity, has the range of 0.85±0.05, andthe camber quantity of the hub 142 has the range of 5.0%±1.0%. Thesolidity can be expressed by the following formula.Solidity=(chord×Z)/2πrwhere 2πr: circumference length when a radius is r, chord: straight linejoining the L.E of the blade with the T.E of the blade, Z: the number ofblades.

Thus, a value of the solidity presented in the present invention maybecome a mean value from the hub and a tip, for example, an integralvalue.

For the axial flow fan 140, as shown in FIGS. 7A and 7B, a rake baseline of each blade 144 formed on the outer circumferential surface ofthe hub 142 is tilted from that formed horizontal to the outercircumferential surface of the conventional hub 42 by a rake anglebetween about 20 degrees and about 23 degrees. Here, the rake anglerefers to an angle determining how much to tilt and form the blades 144on the circumferential surface of the hub 142.

As for a state where the blades 144 are formed on the outercircumferential surface of the hub 142 through the rake angle, as shownin FIGS. 7A and 7B, among the whole length from the outercircumferential surface of the hub 142 to the outer end (i.e. tip) ofeach blade 144, a part from the outer circumferential surface of the hub142 to a predetermined portion of each blade 144 is tilted at the rakeangle, and the other part from the predetermined portion of each blade144 and the tip of each blade 144 is provided with a bulge 146 protrudedtoward a pressure surface. The tip of each blade 144 has the same angleas the rake angle from the outer circumferential surface of the hub 142to the predetermined portion of each blade 144. In this manner, aprofile of the axial flow fan 140 is formed as a whole.

In other words, when the section from the outer circumferential surfaceof the hub to the tip of each blade is divided into two sections, thefirst section performs rotational displacement at the identical angle,and the second section forms a non-linear angle raised toward thepressure surface. The tip (i.e. a section except for the two sections)is adapted to apply an identical value of the first section.

At this point, the outer diameter D of the axial flow fan is 460±2 mm,and the outer diameter d of the hub 142 is 170±2 mm.

Here, a pitch angle, a peak point of a camber, and a sweep angle of eachblade 144 are the same as the pitch angle β, the peak point of thecamber P, the maximum quantity of the camber MC, and the sweep angle αof the conventional blade 44 shown in FIGS. 3A and 3B. Now, the pitchangle, the peak point of the camber, and the sweep angle of each blade144 will be described in detail below.

The pitch angle β of each blade 144 is configured to be linearly changedfrom the hub 142 to the end of the blade 144 within a range between 37degrees and 20 degrees.

Each blade 144 is configured so that the peak point of the camber P isformed at a position corresponding to 70% of a length of a chord in adirection from the front end of the blade to the rear end of the blade,and that the maximum quantity of the camber MC is kept constant at avalue of 0.5% within each radius from the hub 142 to the end of theblade 144.

Furthermore, the sweep angle α of each blade 144 has a range betweenabout 47 degrees and about 49 degrees when a dimensionless radiuscoordinate is less than 0.3 and is linearly increased when thedimensionless radius coordinate exceeds 0.3 to have a range betweenabout 55 degrees and about 57 degrees at the end of the blade.

A change of the noise generated from the axial flow fan configured asset forth above will be described below.

FIG. 8 is a graph showing a state where a noise is changed according toa change of a solidity with respect to axial flow fans of the prior artand the present invention. FIG. 9 is a graph showing a state where anoise is changed according to a change of a quantity of a camber withrespect to axial flow fans of the prior art and the present invention.FIG. 10 is graph showing relation between a (constant) pressurecoefficient, a constant pressure efficiency and a flow rate coefficientwith respect to axial flow fans of the prior art and the presentinvention. FIG. 11 is a graph showing comparison of a state where anoise is changed according to a change of a frequency of an axial flowfan of the present invention with that of an axial flow fan of the priorart.

As seen from the foregoing description and the drawings, the solidityapplied to the present invention has a range of 0.85±0.05 and the camberquantity of the hub has a range of 5.0%±1.0%.

In contrast, the solidity applied to the prior art (Z=3) has arelatively great value compared to that of the present invention, andthe camber quantity of the hub has a relatively small value.

The following description will be made with reference to FIGS. 10 and11.

In the graph of FIG. 10, an upper line shows a comparison of relation ofthe (constant) pressure coefficient and the flow rate coefficient in theaxial flow fan 140 with that of the conventional axial flow fan 40,while a lower line shows a comparison of relation of the constantpressure efficiency and the flow rate coefficient in the axial flow fan140 with that of the conventional axial flow fan 40.

For the axial flow fan 140 according to the present invention, the noisechange was measured depending on the change of the solidity as the ratioof the whole area of the fan 140 to the area of the blades. It was foundthat as a result of the measurement, as shown in FIG. 8, when the ratioof the whole area of the fan 140 to the area of the blades, i.e. thesolidity, was about 0.87, the noise was the lowest. Further, the noisechange was measured depending on the change of the camber quantity ofeach blade of the axial flow fan 140. It was found that as a result ofthe measurement, as shown in FIG. 9, when the camber quantity of theblade 144 was about 0.5%, the noise was lowest.

For the axial flow fan 140 according to the present invention, it can beseen that as shown in FIG. 10, the pressure coefficient and the constantpressure efficiency were enhanced over the conventional axial flow fan40, and that the operation efficiency was also enhanced at the operationpoint according to the enhancement of the pressure coefficient and theconstant pressure efficiency of the axial flow fan 140 as set forthabove.

Further, FIG. 11 is a graph showing comparison of a state where a noiseis changed according to a change of a frequency of an axial flow fan ofthe present invention with that of an axial flow fan of the prior art.As shown in FIG. 11, it can be seen that when having an air volume equalto that of the conventional axial flow fan 40, the axial flow fan 140was subjected to great reduction of the noise in a range between about300 Hz and about 1000 Hz.

As set forth above, the present invention relates to the axial flow fanconfigured so that the number of the blades is two, that a predeterminedrake angle is kept constant in the part from the hub to thepredetermined portion of the blade among the whole part from the hub tothe outer end of the blade and is increased in the pressure surfacedirection in the other part from the predetermined portion of the bladeto the outer end of the blade, and the ratio of the inner diameter tothe outer diameter is between about 0.35 and about 0.4.

Therefore, the axial flow fan of the present invention is designedwithin an optimal design range (that the solidity, the ratio of thewhole area of the axial flow fan and the area of the blades, is about0.87 and that the camber quantity of the hub is about 5.0%), forexample, capable of suppressing increase in intensity of the turbulentflow generated from the surface of each blade, increase in thickness ofthe boundary layer on the surface of each blade and disturbance of theairflow within the region of the hub. As a result, the axial flow fan ofthe present invention can reduce the noise as low as possible andincrease the pressure coefficient and the constant pressure efficiencycompared to the conventional axial flow fan.

Further, the axial flow fan of the present invention can remarkablyreduce the noise within the predetermined frequency range (e.g. betweenabout 300 Hz and about 1000 Hz) with respect to the same air volume asthe conventional axial flow fan.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

For example, the axial flow fan of the present invention may be appliedto a refrigerator or other apparatuses for condensing and evaporating arefrigerant.

Therefore, the above-mentioned description is simply illustrative butnot intended to restrict the invention by limitations of the claims.

1. An axial flow fan comprising: a hub connected with a rotational shaftof a motor; and at least one blade contacting the hub, wherein the bladehas a part from the hub to a predetermined portion of the blade among awhole part from the hub to an outer end of the blade, and the other partfrom the predetermined portion of the blade to the outer end of theblade, the part being equally applied at a predetermined rake angle, andthe other part being raised in a direction of a pressure surface of theblade.
 2. An axial flow fan as set forth in claim 1, wherein a rake baseline of the blade formed within the part from the hub to thepredetermined portion of the blade is tilted by the rake angle of about23 degrees.
 3. An axial flow fan as set forth in claim 2, wherein therake base line of the blade formed on an outer circumferential surfaceof the hub is tilted by the rake angle between about 20 degrees andabout 23 degrees.
 4. An axial flow fan as set forth in claim 1, whereinthe rake angle begins at the outer end of the blade.
 5. An axial flowfan comprising: a hub connected with a rotational shaft of a motor; andat least one blade brought into contact with the hub, wherein a ratio ofan inner diameter and an outer diameter of the axial flow fan is betweenabout 0.35 and about 0.4.
 6. An axial flow fan as set forth in claim 5,wherein the ratio of the inner diameter and the outer diameter is avalue dividing the outer diameter of the axial flow fan by a diameter ofthe hub.
 7. An axial flow fan as set forth in claim 5, wherein thenumber of the blades is two.
 8. An axial flow fan as set forth in claim5, wherein a solidity has a range of 0.85±0.05.
 9. An axial flow fan asset forth in claim 5, wherein the hub has a quantity of a camber of5.0%±1.0%.
 10. An axial flow fan as set forth in claim 5, wherein theouter diameter of the axial flow fan has a range of 460±2 mm.
 11. Anaxial flow fan as set forth in claim 5, wherein the hub has an diameterof a range of 170±2 mm.
 12. An axial flow fan as set forth in claim 5,wherein a noise is greatly reduced between about 300 Hz and about 1000Hz.
 13. An axial flow fan comprising: a hub connected with a rotationalshaft of a motor; and at least two blades disposed around the hub,wherein the blade has a first section where a rake ange is uniform and asecond section where the rake angle is not uniform.
 14. An axial flowfan as set forth in claim 13, wherein the first section of the blade isfrom an inner end of the blade to a predetermined portion of the blade,and the second section of the blade is from the predetermined portion ofthe blade to an outer end of the blade.